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l l "lo ,fs l, INK/Emo 3D LEoN J. Riem RS MILTON L ROSENTHAL TQM UnitedStates @arent @ffice ABSTRACT 0F THE DISCLOSURE A low profile antenna isdisclosed comprising a plate uniformly spaced from a ground plane. Theplate is .ted RF energy at selected opposed points to produce separatecurrent paths in the plate. Polarization may be controled by suitablyphasing the currents.

This is a continuation of application Serial No. 519,178 filed Ian. 6,1966.

This invention relates to antenna systems and methods and means forcoupling to an antenna to provide a prescribed radiation pattern aboutthe antenna of linearly or circularly polarized radiation.

Heretofore, the diret-lion of polarization of radiation transmitted byor detf;;,ted by an antenna system has been determined by theorientation of the elements of the antenna relative to the direction ofthe transmitted or received radiation. For example, it has often beenthe practice to employ at least two separate antenna elements, eachdesigned for transmitting or receiving radio frequency (RF) energy of agiven direction of polarization. These two elements are oriented inspace relative to each other, so that their directions of polarizationcombine to form a resultant direction of polarization as desired. Thus,'5;' energizing two elements with RF energy in the same, or at oppositephase, the direction of the resultant angle of polarization can hedetermined. Furthermore, this direction can be varied by varying theratio of amplitudes of RF energy energizing the two elements. In areciprocal manner, the same two elements can be employed to detect orreceive incident radio frequency energy and respond to particulardirections of polarization of the incident RF energy by weighting thesignals received by each and combining the vieighted signals in theproper phase relationship to make the antenna system responsive toincident RF energy at the particular desired angle of polarization.

The same, or similar structure, has also been employed to transmit orreceive radiation 'which is circularly rolarzed or which has a componentwhich is circularly polarized. ln the case of transmission, this isaccomplished by feeding the two elements in rhase quadrature. lf theantenna system is used to receive incident circularly polarizedradiation, the signals from the elements are detected then combined inphase quadrature. In either event, whether the antenna is used totransmit or receive linearly polarized or circularly polarizedradiation, the structz're i as consisted of separately energizedelements which are oriented with respect to each other in a prescribedrat-ner.

it is one object of the present invention to provide an antenna systemfor transmitting or receiving RF energy of a given predeterminedpolarization employing a single active antenna element.

It is another object of the present invention to provide an antennasystem for radiating` or detecting radio frequency energy employing atransmission line system coupled to the active element or' said antennawhich may Patented Nov. Il, i959 be operated so that the antennatransmits or detects RF energy which is linearly polarized in'anydirection or right or left-hand circularly polarized.

It is another object of the present invention to provide such an antennaand transmission line system, including a single active element.

It is another object of 'l e present invention to provide a lowsilhouette antenna system, including a single active element with atransmission system coupled thereto and operated so that the anlennasystem transmits or receives preferentially radiation ir. any givendirection of linear or sense of circular polarization.

It is another object of the present invention to provide an antennasystem, the active elements of which follow the contours of the antennaground plane and are :fparated therefrom by a small fraction of awavelength of operation of the antenna.

In accordance with the nncipal feature of the presentr invention, aradiating clement is disposed just above the ground plane, through w ithtransmission lines proiect for coupling RF energy fo o. from selectedpoints or areas on the element. The number of selected points on theelement ineludeat least two pair which are coured to transmit or rexiveequipment, so that the system transmits or receives RF energy which islinearly polarized in any predetermined direction or circularlypolarized with either lertor right-hand sense. In preferred embodiments,the active antenna element is an eier-Iically conductive plate or filmwhich conforms'to the :om tours of the ground plate and is separated atall points therefrom by a constant distance which is preferably a smallfraction o a wavelength of the frequency of operation. For errar-spie,the separation may be as small a ten thousandth of a Wavelength. Thepoints on the plate to which the transmisdon lines couple are preferablyin pairs, each pair defining a line such that the lines dened by dierentpairs are orthoeonal in the plane of the plate. In addition, thetransmission me system to which the plate couples is such that eachpoint of a pair is in opposte phase with respect to the other point inthe sazne pair and means are provided for switching the phaserelationship and/or attenuatng RF energy, transmitted to or detected atthe points on the plate so that polarization is linear in any directionor circular in either sense.

The shape of the radiating lm or plate, as mentioned above, preferablyis such that the plate follows the contours of the ground plane and isseparated therefrom at all points by the same distance. Beyond thislimitation, however, the plate may have just about any shape. It ispreferred, however, that the points or areas on the plat: to which the'ransmission lines couple be located close to the perimeter of the plateand that the perimeter be at least a wavelength in length.

Other features and objects of the present invention will be apparentfrom the following specic description taken in conjunction with :hefigures in which:

FIGURE l is a pictorial diagram of the plate antenna and block diagramof the transmission line and transmitter or rccei ver system coupledthereto;

FIGURES 2a, b, c and d illustrate a sguare plate autenna, the comers ofwhich couple to the transmission lines and show the type of polarizationobtained when these points are energized in particular arzrolitude andphase relationships;

FIGURE 3 illustrates an embodiment of the invention including the flatplate mounted on a cylindrical ground plane, which may represent, forexample, the surface of a vehicle such as an airplane, and;

FIGURES 4 and 5 are curves showing the patterns of radiation atdilfere'it directions of polarization for the antenna system illustratedin FIGURES 1 and 3.

t l l Zwem-.s refinements-ln.

Turning first to FIGURE l, there is shown the principal parts of anantenna system embodying features of the invention. The structureincludes ai; antenna plate 1 disposed just above the ground plane 2 sothat the plate follows the contour of the `ground plane and is spacedfrom the ground plane at all points by a substantially constant distanceS, which is on the order of less than a tenth of a wavelength of thefrequency of operation of the antenna. Tue plate 1 as illustrated issubstantially square and of a sizesuch that the perimeter of the plateis at least one wavelength of the frequency of operation. The squareshape is illustrated for purposes of example and is not a limitation.For example, the plate may be rectangular, circular, oval. or just aboutany shape awrefl. However, it is preferred that the plate have twotransverse Cir-f-nsions which are approximately equal or at least of thesame order o? magnitude.

Four points on the plate, denoted A, E, C and D are coupled to separatetransmisson lines which extend on the opposite side of the groud plane 2from the plate. These transmission lines are cach represented in FIG-URE l by double lines extending from the points A, B, C and D throughopenings 4 to 7 in the ground plane 2. The transmission lines 8 to 11may be waveguides, 2-elcment transmission lines,` coaxial line,stripline, or any of the well-known .forms of transmission linessuitable for conducting the RF energy.

The transmission lines 8 to 11 couple to a transmission or receivesystem 12, which is designed and operated to meet the followingcondition. Points A and C are in opposite phase and points B and D arein opposite phase. Furthermore, either B and A or D and A are in thesame phase. When these conditions are met, the antenna system includingthe antenna and system 12 either transmits or receives linearlypolarized radio frequency energy. The direction of polarization isillustratcd by the sketches in FIGS. 2a and 2b. FIGURE 2:. illustratesthe direction of the resulting polarization in the case when points Aand B are in the same phase. The resultant polarization vector 14represents the sum of vectors 15 and 16. Vector 15 representspolarization that would be produced by an RF current flow between pointsA and C and vector 16 represents polarization that would be produced bycurrents flowing between B `nd D in the phases mentioned above.l Thetransverse dirvtion of polarization represented by vector 1S in FIG. 2bis produced when points A and D are at the same phase. ln this case,vector 16 is reversed relative to the direction in FIG. 2a, and so theresultant polarization direction is switched to the transverse position.

The transmission system 12 may be so designed that during operation theresultant polarization direction, such as represented by vectors 14 or18 may be switched by the simple expedient of reversing the phasebetween a pair of points on the surface of the plate such as pair AC orpair BD. This may be accomplished employing an electrical or amechanical phase shifter.

The antenna plate illustrated in FIGS. l and 2, aS already mentioned, isshown as a square and the points designated A to D are at the corners ofthe square, close to the periphery of the plate. As a result, the pairsof points AC and BD define orthogonally related polarization directions.Furthermore, since the plate is symmetricai on diagonals and thetransmission lines which couple to the points A to D are equal in allrespects, the patterns of radiation representing each of thepolarization directions AC and BD are equal. Accordingly, the magnitudeof the vectors such as 15 and 16 representing these radiation patternsare equal and orthocnal. This explanation of the operation is o'ered asan attempt to explain or justify the empirical results. It is not,however, suggested that the antenna functions entirely in such a simplemanner and that all operations of such an antenna, or a similar antenna,can be explained by such a simple analog of the antenna.

Assuming that the above analog depicting operation of the antenna iscorrect and can be extended to predict and/or explain operation when thepoints A to C are 'not disposed at the corners of a square or thetransmission lines coupled to these points are not equal, then theexpedient of s 4'itchin hase betwce a r ts such as AC o Bllgwiil notcause the resultant polarizaion direction to switch to the transversedirection. For example, if the transmission lines 8 and 10, which coupleto points A and C, respectively, are more lossy than the transmissionlines 9 and 11 which couple to points B and D, respectively, then thevector 15 will be of smaller magnitude than vector 16. The resultant oftwo such unequal vcctors will not be switched to the transversedirection by the mere expedient of switching phase of one of thevectors. ln fact, the resultant will switch to a dihw tion which is lessthan 1 from the original direction of the resultant. Similarly, if twoof the points, such as A and C, are closer together than the points Band D, the same thing will happen; namely, the resultant polarizationvector will switch in ('irection less than 90 when the phase between apair of the points is switched.

In accordance with another feature of the invention. the transmissionsystem 12 may be so designed that the resultant polarization vectorrotates to the right, illustrated in FIG. 2c, or to the left, asillustrated in FIG. 2d. Thus, the antenna system will transmit orreceive radio frequency energy which is circularly polarized, 0r atleast has a strong component which is circularly polarized. It has beenfound that the left-hand circularly polarized response of the antennasystem illustrated in FlG. 2c will be obtained when the pairs of pointsAC and BD are energized so that the vectors 15 and 16 in the analogconstructed as already described, are in phase quadrature, `with vector1S leading vector 16 in phase by 1r/2 radians. When this occurs, theresultant polarization vector Z'i, as viewed looking toward plate 1 andthe ground plane 2, will rotate clockwise as shown in FSG. 2c. On theother hand, when vector 16 leads vector 15 by ir/2 radians, the circularpolarization is in the opposite sense, as shown by vector 22 in FIG. 2d.Again, it will be remembered that the analog constructed here t0 explainthe observed operation of the antenna system is olered for convenienceand does not preclude another explanation of the same observedphenomena. based upon D another or a different analog of operation.

Returning again to FIG. I, and more particularly to details of thetransmission system 12, there is shown in a general form a system foroperating the antenna either to transmit or to receive in any of themanners a1- ready described with reference to FIGS. 2a to 2d. For fourtransmission lines 8 to 11 which couple to the points A to Drespectively. Each of these transmission lines extends to a balunstructure, the length of each line between the balun struct-ure and thepoint on the plate 1 being electrically the same. Thus, points A and Care coupled by transmission lines 8 and 10, respectively, to balunstructure 23 and points B and D are coupled via transmission lincs 9 and11, respectively, tc balun structure 24. The balun structures 23 and 24are so constructed that they divide power in opposite phase between thetwo transmission lines connecting the balun structurel to the points onthe antenna plate 1 and, in reciprocal?, fashion, these balun structurescombine radio frequencyi energy of opposite phase conducted from thepoints so that the energy adds. Art example of a balun structure whichwould be suitable is the magic Tec hybrid which would be used if thetransmission lines 8 to 11 are waveguides. Another type of balunstructure used fre-l quendy with multi-element transmission lines suchas b cficial lino or tr l' the hybrid referred to as a hybrid ring ormore commonly the rat lace. Any of these may be employed with theappropriate transmission line to perform the function of the balunstructures 23 and 24.

In the simplest embodiment of the invention, the balun structures 23 and24 are coupled by appropriate transmission lines 2.5 and 26 to a powerdivider 27 which couples to a transmitter or receiver 28, depending uponwhether the system is used to transmit or receive. The power divider 27and the transmission lines coupling the power divider to the balunstructures are such that the balun structures are fed equal power duringtransmission cr such that equal power from the balun structures arecombined and fed to the receiver when the system is employcd to receive.If additional polarization modes of operation are desired and it isdesired to switch from one polarization direction to another, asdescribed above with reference to FIGS. 2a to 2d, means such as a phaseshifter 29 is provided between one of the balun structures 23 or 24 andthe power divider 27. For example, when it is desired to switch linearpolarization direction from one direction to the transverse direction,as shown in FIGS. 2a and 2b, then the phase shifter 29 must be operatedto reverse the phase at balun structure 14 relative to balun structure23 and this is the case whether the system is used to transmit orreceive. For this purpose, phase shifter 29 may be .lectrisally ormechanically operated to shift the relative vphases at the balunstructures by 180. On the other hand, when circularly polarizedtransmission or reception -by the antenna system is desired, the phaseshifter 27 must shift phase so that radio frequency energy at the baluzistructures 23 and 24 is in quadrature. For this purpose, he phaseshifter 29 may be designed so that when operated one way or another itwill shift phase 90 or 270 and, thus, produce right-hand or left-handpolarization of the antenna system. If it is dea sired to switch fromlinear to circular polarization, the phase shifter may be designed toproduce phase differences at balun structures 23 and 24 of 0 or 90.

Typical radiation patterns obtained with an antenna structure such asdescribed above, with reference to FIGS. l and '2., are shown in FIGS. 4and 5. Each of the FIGS. 4 and S include plots of relative radiationintensity in decibel; vs. direction angle coordinates. The direction 4angles are defined as 0 and p which are orthogonal angular coordinatestaken as illustrated in FIG. 3. FIGURE 4 shows tlc radiation patterns asa function of decibels in each of the angular directions 0 and (brokenand solid lines, respectively) for radiation linearly polarized in the odirection and FIG. 4 shows the same type patterns for radiation linearlypolarized in the e direction.

The radiation patterns shown in FIGS. 4 and 5 are typically thoseobtained employing, for example, a inch square plate or film antenna 31mounted centrally on a metal ground plane cylinder 32, which is 4 feetin diameter and 3 feet high. The radiation pattern is obtained frommeasurements made when the antenna is energized as described above withreference to FIGURE 1 at 250 mc. The ground plane cylinder 32 mightrepresent the fuselage or external confirmation of some part of amissile or an airplane. The plate antenna 31 is preferably fixed to theoutside of this surface by a suitable dielectric adhesive so that it isspaced a few thousandrhs of a wavelength (at 250 mc.) from the surfatall points. Since the periphery of the plate 31 is about 60 inches,quite clearly, the periphery is more than a. wavelength nt the operatingfrequency of 250 mc. A transmission line structure such as alreadydescribed above with reference tc FIG. l, preferably is located insidethe ground plane cylinder 32 and energizes the antenna as alreadydescribed, so that radiation issuing from the antenna plate is polarizedin e 0 direction er in the o direction. Perpendicular to plate 3l, 0polarization is substantially parallel to axis 33 of cylinder 32,whereas o polarization is substantially parailel 'ro the circumferenceline 34 of the cylinder. The coordinates 9 and qb defining a spatialpoint 35 at unit distances 36 are measuredas demonstrated in FIGURE 3and it is these measurements which are plotted as the abscissa in theradiation paticrus shown in FIGS. 4 and 5. The ordinate (Db) is ameasure of the intensity of the polarized radiation at the unitdistance.

As'can be seen from FIGS. 4 and 5, the intensity of polarized radiationis greatest in the direction directly perpendicular to the plate 31extending from the origin 37 along a line out of the page. Both of thecoordinate angles 0 and p are measured from this line and so along thisline, both 0 and are zero. Each angular value of 0 and p is defined by aline from the origin 37 to the point in space such as '3S at the unitdistance. As can be seen from the radiation patterns, in both the andthe d coordinates, substantial intensities of radiation polarized ineither direction are produced at 0 or qb equal to or -90. In fact, at-lor 90 in either case, the radiation level is only down between 20 to30 db. Thus, the radiation pattern if depicted in three dimensions wouldappear to wrap around the radiating plate 31, somewhat similar to acardioid pattern.

Various embodiments of the present invention may be combined to performa multitude of functions. For exarn ple, a plaze such as 31 could bemounted almost ush with the surface of an airplane and separatedtherefrom by only a small fraction of an inch or less and energized fromwithin the airplane to create radiation patterns ex tendingperpendicular from the plate of the various linear or circularpolarizations described and the polarization direction could be switchedreadily between dierent types of linear or circular polarization. Thisstructure would be an advantage in, for example, a weather radar systemon board an airplane, where a beam of circularly polariycd radiation islaunched with some directivity to detect rain. It is the uniquecharacteristics of rain drops to reiiect much oi the incident circularlypolarized radiation and reverse the direction of circular polarization.Thus, the antenna system could be used to transmit circularly polarizedradiation rzone sense and an instant later, or simultaneously, operatedto receive echo signals polarized in the opposite sense, just as alreadydescribed above with reference to FIG. l and FIGS. 2c and d. Of course,the same antenna structure could be employed to transmit or receivelinearly polarized radiation, as already described.

Many other uses and modifications of various features of the presentinvention will be apparent to those skilled in the art. Accordingly, theembodiments described herein are made only by way of example and do notlimit the scope of the invention set forth in the accompanying claims.

What is claimed is:

1. An antenna system comprising a ground plane and a layer of conductivematerial disposed opposing the ground plane and substantially uniformlyspaced therefrom,

said layer serving to conduct separate RF current paths which cross, and

a separate transmission line coupled to the layer at each end of eachcurrent path,

whereby the antenna sysem has a directional pattern of RF radiationhav'ng a. rotating direction of polarization when the cu rreuts n theseparate paths are not ir. phase.

2. An antenna system as in claim 1 andin which,

said uniform spacing is substantially less than a wave length of said RFradiation.

3. An antenna system as in claim 1 and in which there are four of saidseparate transmission lines coupled tn said layer, each at a differentpoint.

4. An antenna system as in claim 3 and in which, said points detine asquare.

5. An antenna system as in claim 4 and in which,

said points are at diago Jal corners of said square and said points atdiagonal corners are at opposite RF phase.

6. An a1 tenna system as in claim 1 and in which,

said RF currents in separate paths are in phase n uadrature.

7. An antenna system as in claim 1 and in which,

said transmission lines are part of a transmiring s5stem for energizingsaid antenna system to produce said directional pattern of RF radiation.

8. An antenna system as in claim 1 and in which,

said transmission lines are part of a receiver system responsive to saiddirectional pattern of RF radiation.

9. An antenna system comprising a ground plane, a layer of electricallyconductive material which is continuous in two dimensions defining anIarea of the layer, the layer being disposed opposing said ground planeand substantially uniformly spaced therefrom, and at least fourtransmission lines, each coupled to a different point along theperimeter of said area of conductive material, whereby said antennasystem has a directional pattern of polarized radiation.

10. An antenna system as in claim 9 and in which said pattern is ofgreatest intensity in direction substantially perpendicular to saidlayer of conductive material.

11. An antenna system as it: claim 9 and in which said uniform spacingis substantially less than a wavelength of said. radiation.

17.. An antenna system as in claim 9 and in which the perimeter of saidarea of conductive material is at least as great as a wavelength of saidradiation.

13. .An antenna system as in claim 9 and in which said perimeter of saidarea of conductive material is substan tially coincident with the edgeof said layer of conductive material.

14. An antenna system as in claim 9 and in which said four differentpoints are spaced at comers of a square.

15. An antenna system as in claim 414 and in which said points are atdiagonal corners of `said square and couple to transmission lines suchthat the diagonal points are energized at opposite phase of saidradiation.

16. An antenna system as in claim 15 and in which the points at oppositediagonal corners of said square A 8 couple to transmission lines whichare part of a transmission line system such that the antenna systemresponds radiation incident upon the conductive plate which energizesopposed diagonal points of said square in opposite phase.

17. An antenna system as in claim 16 and in which said transmission linesystem includes means for switching phase of at least one pair of saiddiagonally opposed points of said square.

18. An antenna system as in claim 16 and in which said transmission linesystem includes means for switching phase response of at least one pairof said diagonally opposed points of said square.

19. An antenna system as in claim 15 and in which two of said diagonallyopposed points of said square are energized in phase quadrature withrespect to the other two points.

20. An antenna system as in claim 16 and in which said transmission linesystem is such that the antenna system responds to radiation incidentupon the conductive plate which energizes two o said diagonally opposedpoints of said square in phase quadrature with respect to the other twopoints.

References Cited UNITED STATES PATENTS 2,791,769 5/1957 Lindenblad343-769 2,826,756 3/1958 Cary 343-829 2,990,547 6/1961 McDougal 343-9083,086,204 4/ 1963 Alford 343-769 3,165,743 l /1965 Hatkin 343-767 X ELILIEBERMAN, Primary Examiner U.S. C1. X.R. 343-708, 857, 908

